Rho Kinase Pathway Alterations in the Brain and Leukocytes in Huntington's Disease.

Huntington's disease (HD) is a fatal neurodegenerative disease caused by an expanded polyglutamine tract in the huntingtin gene. Therapeutic approaches targeting mutant huntingtin (mtHtt) or its downstream toxic consequences are under development, including Rho kinase pathway inhibition. We investigated the messenger RNA (mRNA) expression of Rho kinase pathway genes, including RhoA (Ras homolog family member A), ROCK1 (Rho-associated kinase1), PRK2 (protein kinase C-related protein kinase 2), Profilin1, cofilin1, MYPT1 (myosin phosphatase target subunit 1), and LIMK1 (LIM domain kinase 1) in HD human blood leukocytes, postmortem brain, and in R6/2 HD mouse brain tissue using qPCR. RhoA, ROCK1, PRK2, Profilin1, cofilin1, and MYPT1 were significantly increased in HD blood compared to controls. In frontal cortex of HD postmortem brain tissue, the expression of RhoA, ROCK1, PRK2, Profilin1, and MYPT1 were also significantly increased. In the brain from 4-week-old R6/2 mice, the expression of Rock1, Prk2, Cofilin1, and MYPT1 was significantly increased while RhoA, Rock1, Profilin1, Cofilin1, and Mypt1 were increased and Limk1 mRNA decreased in 13-week-old R6/2 mice. Western blot analysis using human postmortem tissues for ROCK1 and Profilin1 demonstrated significantly increased protein levels, which correlated with the mRNA increases. Collectively, we have shown the panel of Rho kinase pathway genes to be highly altered in human HD blood, postmortem brain tissue, and in R6/2 mice. These studies confirm that HD upregulates the Rho kinase pathway and identifies mRNAs that could serve as peripheral markers in HD patients and translational markers in HD mouse models.

A systems-level "misunderstanding": the plasma metabolome in Huntington's disease.

OBJECTIVE: Huntington's disease (HD) is a rare neurodegenerative disease caused by the expansion of an N-terminal repeat in the huntingtin protein. The protein is expressed in all cells in the body; hence, peripheral tissues, such as blood, may recapitulate processes in the brain. The plasma metabolome may provide a window into active processes that influence brain health and a unique opportunity to noninvasively identify processes that may contribute to neurodegeneration. Alterations in metabolic pathways in brain have been shown to profoundly impact HD. Therefore, identification and quantification of critical metabolomic perturbations could provide novel biomarkers for disease onset and disease progression. METHODS: We analyzed the plasma metabolomic profiles from 52 premanifest (PHD), 102 early symptomatic HD, and 140 healthy controls (NC) using liquid chromatography coupled with a highly sensitive electrochemical detection platform. RESULTS: Alterations in tryptophan, tyrosine, purine, and antioxidant pathways were identified, including many related to energetic and oxidative stress and derived from the gut microbiome. Multivariate statistical modeling demonstrated mutually distinct metabolomic profiles, suggesting that the processes that determine onset were likely distinct from those that determine progression. Gut microbiome-derived metabolites particularly differentiated the PHD metabolome, while the symptomatic HD metabolome was increasingly influenced by metabolites that may reflect mutant huntingtin toxicity and neurodegeneration. INTERPRETATION: Understanding the complex changes in the delicate balance of the metabolome and the gut microbiome in HD, and how they relate to disease onset, progression, and phenotypic variability in HD are critical questions for future research.

PRECREST: a phase II prevention and biomarker trial of creatine in at-risk Huntington disease.

OBJECTIVE: To assess the safety and tolerability of high-dose creatine, the feasibility of enrolling premanifest and 50% at-risk subjects in a prevention trial, and the potential of cognitive, imaging, and blood markers. METHODS: Sixty-four eligible consenting participants were randomly allocated (1:1) to 15 g twice daily of creatine monohydrate or placebo for a 6-month double-blind phase followed by a 12-month open-label extension. Subjects included premanifest (tested) and at-risk (not tested) individuals without clinical symptoms or signs of Huntington disease (HD). Primary outcomes were safety and tolerability. Exploratory endpoints included fine motor, visuospatial, and memory performance; structural and diffusion MRI; and selected blood markers. RESULTS: Forty-seven HD carriers and 17 non-HD controls were enrolled. Fifteen discontinued treatment (2 assigned to placebo); all were followed for the entire study period. Primary analysis was by intent to treat. The most common adverse events were gastrointestinal. Neuroimaging demonstrated treatment-related slowing of cortical and striatal atrophy at 6 and 18 months. CONCLUSION: We describe a design that preserves the autonomy of subjects not wanting genetic testing while including controls for assessing the specificity of treatment effects. Our results demonstrate the feasibility of prevention trials for HD and the safety of high-dose creatine, provide possible evidence of disease modification, support future studies of creatine, and illustrate the value of prodromal biomarkers. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that high-dose creatine is safe and tolerable.

A tale of two factors: what determines the rate of progression in Huntington's disease? A longitudinal MRI study.

Over the past several years, increased attention has been devoted to understanding regionally selective brain changes that occur in Huntington's disease and their relationships to phenotypic variability. Clinical progression is also heterogeneous, and although CAG repeat length influences age of onset, its role, if any, in progression has been less clear. We evaluated progression in Huntington's disease using a novel longitudinal magnetic resonance imaging analysis. Our hypothesis was that the rate of brain atrophy is influenced by the age of onset of Huntington's disease. We scanned 22 patients with Huntington's disease at approximately 1-year intervals; individuals were divided into 1 of 3 groups, determined by the relative age of onset. We found significant differences in the rates of atrophy of cortex, white matter, and subcortical structures; patients who developed symptoms earlier demonstrated the most rapid rates of atrophy compared with those who developed symptoms during middle age or more advanced age. Rates of cortical atrophy were topologically variable, with the most rapid changes occurring in sensorimotor, posterior frontal, and portions of the parietal cortex. There were no significant differences in the rates of atrophy in basal ganglia structures. Although both CAG repeat length and age influenced the rate of change in some regions, there was no significant correlation in many regions. Rates of regional brain atrophy seem to be influenced by the age of onset of Huntington's disease symptoms and are only partially explained by CAG repeat length. These findings suggest that other genetic, epigenetic, and environmental factors play important roles in neurodegeneration in Huntington's disease.